Long time reader first time poster and I used the search feature before posting.

I have a 92 Prostar 190 with the 351w HO engine. The 4010 carburetor has started to show its age so I bought a new brand 4160, the correct one designed for 351W.

Here’s the problem. It runs really rich at idle, and runs best with the idle screws all the way in. I know this is not correct, and it is getting fuel from somewhere else. Thinking I got a bad carb, I returned the first 4160 and got a replacement. I followed the directions and watched the video on the Holley website on how to adjust the idle screws several time and have a good idea on how this stuff works. It is running so rich that when I pull the PCV hose off the spacer the rpm rises. In the process of trouble shooting I put the 4010 back in and those idle mixture screws kill the motors when screws and screwed all the way in.

I know that I do not have a blown power valve being that it is brand new. I can’t see any fuel pouring out of the ventures on idle. I am stumped. The only thing I haven’t checked is the fuel pressure, but the 4010 works just fine. Only reason I replaced it is that it started to get leaky seals. I never thought I would say but the 4010 seems to work better.

This is the second brand new 4160 I have had on the boat in as many weeks. I did double check the power valve on the new 4160, and it is a 2.5 and good. I am stumped. The only thing I can think of is fuel pressure is too high, but it ran perfect minus a few small leaks because of the old rotten seals on the 4010. I am checking the fuel pressure tomorrow. I called the Holley help line, they were no help?????? I did put the old 4010 back on to ski tonight and it ran perfect.